The present invention relates to a drill for drilling of preferably metallic work pieces and a cutting insert for use in this drill.
Hitherto known drills comprise either rectangular, rhombical or triangular cutting inserts. When using drills having rectangular cutting inserts problems often arise with deflections of the drill shank at drilling in the solid work piece due to the cutting inserts having straight unbroken cutting edges. One of the cutting inserts must overlap the center of the drill which often results in that the engagement of one cutting edge with the work piece becomes shorter than the engagement of the other cutting edge. This results in unevenly acting cutting forces and therefore the drill may cut unbalanced and may give the hole tolerance faults. The straight long side of the rectangular cutting insert may cause vibrational damages on the exit side of the drill hole. In drills carrying triangular or rhombical cutting inserts broken cutting edges are often used and therefore it is possible to achieve a balanced cutting engagement. The triangular or rhombical shape, however, gives the cutting insert, especially at smaller dimensions, a small strength and a small space for chip breakers inside the cutting edges, primarily depending on the provision of a central securing hole. A fractured cutting insert may destroy both the work piece and the drill shank.
The present invention relates to a drill and a cutting insert therefor which solves the above mentioned problems.